In shaft furnaces, particularly in blast furnaces, pressurized hot gas, typically pressurized hot air, is blown into the furnace for aiding the reduction of ore in the shaft furnace.
Conventionally, a circumferential bustle pipe is arranged in the tuyere band around the outer casing of the shaft furnace, at a certain distance therefrom. The gas is fed from the bustle pipe through a tuyere stock row, where it is blown into the shaft furnace. A tuyere stock is generally provided with compensators for compensating for relative movement between the bustle pipe and the shaft furnace. Such a conventional bustle pipe arrangement is e.g. known from WO 86/05520.
It has been suggested to inject gas into the shaft furnace, not only at the upper hearth level, but also in a region above the melting zone, also referred to as the “lower shaft”. Lower shaft injection necessitates a further bustle pipe arrangement for feeding gas to the individual injection points in the lower shaft.
The conventional bustle pipe arrangement, as described above, has been considered. Although such a solution has the obvious advantages of being a known and tested solution, it also has a number of drawbacks. Indeed, the considerable weight of this arrangement makes it difficult to arrange at the level of the lower shaft. Also, the cumbersome design of the conventional bustle pipe arrangement limits the number of injection points.
Another contender for a bustle pipe arrangement for injection at the lower shaft level is the so-called “Midrex”-type gas injection, which comprises a circumferential distribution channel built into the furnace wall, as illustrated by U.S. Pat. No. 6,146,442. This allows increasing the number of injection points. However, this solution is difficult to adapt to existing shaft furnaces and introduces some additional risks as to wear of the refractory material, in particular in the wall separating the distribution channel from the furnace chamber. A further non-negligible concern is the statics of the furnace. Indeed, the structure of the furnace is weakened by the “Midrex”-type construction.